In recent years, plasma display panels (hereinafter referred to as “PDPs”) have attracted considerable attention as large- and flat-screen and low-profile display devices. At the present, ac-drive coplanar-discharge type PDPs (hereinafter referred to as “ac coplanar-discharge type PDPs”) are dominant. The ac coplanar-discharge type PDP is an imaging device having a large number of small discharge spaces (discharge cells) sealed between a pair of glass substrates.
In the PDP, plasma is created by discharge of gases (discharge gases) contained in the discharge cells, and ultraviolet rays from the plasma excite phosphors to emit visible light and thereby to form an image display. There is another method of forming an image display by using a light emission directly from the plasma.
Rare gases (particularly a mixture of Ne and Xe gases) have been chiefly used as discharge gases, one of materials of the plasma display devices. Japanese Patent Application Laid-Open No. Hei 6-342631 (laid open on Dec. 13, 1994) discloses the use of a mixture of three gases He, Ne and Xe. Here, the ratio in volume of He to Ne is selected in a range of from 6/4 to 9/1, and Xe is selected in a range of from 1.5% to 10% by volume of the total of the discharge gases. However, there is a problem in that an excessive amount of He shortens lifetime of the display device. Japanese Patent Application Laid-Open No. 2000-67758 (laid open on Mar. 3, 2000) discloses a technique which controls crosstalk between adjacent discharge cells by using a mixture of three gases He, Ne and Xe and thereby increases a drive margin of a sustaining voltage. Japanese Patent Application Laid-Open No. Hei 11-103431 (laid open on Apr. 13, 1999) discloses a technique which realizes a long lifetime, stable driving voltages and proper brightness properties by using a mixture of three gases He, Ne and Xe with He and Xe being equal in concentration. It has been reported in N. Uemura, et al. “Kinetic Model of the VUV Production in AC-PDPs as Studied by Time-resolved Emission Spectroscopy,” Proceedings of IDW '00 (The 7th International Display Workshops), pp. 639–642 (2000) that ultraviolet ray generation efficiency is improved by using a mixture of three gases He, Ne and Xe.
Improvement in luminous efficiency (1 m/W) is desired in development of PDPs. The luminous efficiency is determined by initially dividing a brightness value (or a luminance) (cd/m2) by an electric power (W/m2) required to excite a unit area to provide the above brightness value, and then correcting the obtained quotient by using a solid angle (steradian) subtended by a measurement system as viewed from the light source. Since a discharge gas has a great influence on generation of ultraviolet rays, its setting is important for the improvements of the luminous efficiency. The conditions of plasma change greatly depending upon the composition and pressure of the discharge gas, and consequently, the luminous efficiency also changes greatly. However, in the case of developing a plasma display intended for practical use, the plasma display should be excellent in other performances comprehensively as well as the improvement of the luminous efficiency. When the composition and pressure of the discharge gas are changed to improve the luminous efficiency, lifetime may be shortened, and driving may be unstable. Further, for practical use, high definition, high brightness, low cost and so forth are strongly demanded. Thus, it is necessary to take into consideration other conditions (driving conditions, cost, etc.) in addition to the composition and pressure of the discharge gas, in the development of the plasma display of practical use.